We have an XP4 1K that lost a brake pad after about 1500 Miles. Looked into it and the axle nut was just loose enough that when the hub kept hitting, it would spin the axle nut. Eventually it cut the ends off the cotter pin. Once the pin was gone, the nut got loose enough for the wheel to rip the pad out of the caliper.
We checked all of our axle nuts after that. Here is photo of another one with same mileage about to do the same thing. One end already sheared off, the other end hanging on by a thread. Both were on the driver rear tire.
Guess I will add this to the list of things to keep an eye on.